This invention relates to valves, sometimes known as pinch valves, in which a tubular resilient member provides a passage for the flow of fluid through the valve and is arranged to have its opposed side walls squeezed together to control the flow through said passage.
Such valves have the advantage that the valve can be closed without the use of sliding seals which may wear and allow leakage from the valve. But the reliability of the valve over long periods is also affected by the pressure force that is applied to the tubular member to hold the valve passage closed and the effect that this can have on the eventual re-opening of the passage. It is for example possible that after the valve passage has been closed for a long period it may not reopen or not reopen fully when the closing pressure is released, whether due to adherence of the contacting passage walls to each other or due to the material of the tubular member acquiring a permanent deformation or set.
An arrangement has been proposed in which a series of individual elements are fixed to the tubular member at angularly spaced positions and are displaced radially to open and close the valve but this requires a complex and therefore expensive mechanism to co-ordinate their movements.